The present invention relates to a system for accurately controlling a cutter for cutting a thread chain or binding on a sewing machine.
In the garment industry, garments are finished by applying a binding to the edge of the garment and sewing it in place or by applying an overedge stitch referred to in the art as a thread chain. After the garment passes beyond the needle, the stitches continue to be applied to the edge of the garment to attach the binding or to form the thread chain. At some point, depending on the manner in which the garment is finished, a cutter must sever the binding and the stitches from the portion sewn to the garment or the thread chain from the edge of the garment.
An important requirement of any cutting system is that the length of the thread chain or the binding that remains attached to the fabric, after cutting, be uniform and independent of machine speed and cutter reaction time.
In the prior art, stitch counting is used to control the operation of the cutter. The prior art uses an electric eye which senses the presence or absence of the fabric material. After the fabric passes a distance beyond the electric eye, and the requisite number of stitches are sewn, the cutter is triggered. As can be appreciated, since it takes a finite time for the cutter to react and a time interval elapses for the edge of the material to pass from the electric eye to the cutter, the triggering of the cutter must be properly timed so that the binding or the thread chain is cut at the edge of the material. While, such prior art systems can be adequately set to cut the binding or thread chain for a given sewing machine speed, if the speed of the machine increases, the cutter may react too slowly and cut through the material. This results from the fact that more stitches will be sewn during the cutter reaction time for a faster machine speed.